1. Field of the Invention
The present invention relates to a solenoid valve incorporating a chamber.
2. Description of the Prior Art
FIG. 6 shows a longitudinal sectional view of a solenoid valve in the prior art. Reference numeral 101 denotes a housing made from synthetic resin, having an output port 102 and an input port 103. A negative pressure is to be imposed to the output port. The phrase "negative pressure" in this specification and Claims means "pressure lower than the atmospheric pressure". Reference numeral 104 is a cover made from synthetic resin, in which a coil 105 is installed. A magnetic plate 106 (made from iron) is disposed between the housing 101 and the cover 104 to form a magnetic path together with a core 107. A magnetic yoke 108 (made from iron) forms a magnetic path together with the plate 106. The yoke 108 has a substantially U form.
A connector 110 for supplying electric power to the coil 105 has a hole 109, into which an external socket (not shown) shall be inserted. A first channel 111 disposed in the housing 101 communicates with the output port 102. The output port 102 functions as a negative pressure imposing port. A second channel 112 disposed in the housing 101 communicates with the input port 103.
The core 107 has a coaxial pin 113, which is disposed so that a part thereof projects from one end of the core. A plunger 114 is set on the pin 113. A valve element 115 is disposed at one end of the plunger 114. A spring 116 is disposed between the core 107 and plunger 114, which urges the valve element 115 towards a face of the housing 101 to close the first channel 111. A plate spring 117 is disposed on the plunger 114, which has a sealing element 118 at its peripheral portion. The solenoid valve has a seat 119, for fixing the solenoid valve to a fixing portion (not shown) of an external apparatus. Reference numeral 20 denotes a bolt for fixing the solenoid valve to the fixing portion.
The operation of this conventional solenoid valve is described below.
When electric power is not supplied to the coil 105 from the external power source, the valve element 115 of the plunger 114 is urged by the resilient force of the spring 116 towards a face of the housing 101, so as to close the communicating portion between the first and second channel 111, 112. As a result, the communicating channel between the output port 102 and the input port 103 is closed.
Starting from this state, when electric current is supplied through the coil 105, a magnetic field is induced to move the plunger 114, resisting against the resilient force of the spring 116, to separate the valve element 115 from the face of the housing 101. As a negative pressure is imposed at the output port 102, the fluid supplied into the input port 103 is released from the output port 102, after passing though the first and second channels 111, 112.
In general, electric current is intermittently supplied to the coil 105 so as to control to open and close intermittently the communicating portion between the first and second channel 111, 112. At each opening and closing of the channels, an operation sound is caused by the movement of the solenoid valve, and a flow sound is caused by the opening and closing of the channels. And they propagate to an external apparatus connected with the input port 103. Sound, having a frequency equal to the eigenfrequency of the external apparatus resonates in the apparatus, and a troublesome resonating sound is generated.
In the case when the length of the piping connecting between the input port 103 and the external apparatus (not shown) is an even number multiplied by one quarter of the wave length of the eigenfrequency, this frequency component of the sound resonates in the piping. Namely the sound is amplified in the piping, therefore the resonating sound in the external apparatus further increases.
Moreover, the intermittent opening and closing of communicating part between the first and second channels 111, 112 causes a pulsation of the fluid flow from the second channel 112. The energy of this pulsation causes a mechanical vibration of the piping connecting the input port 103 and an external apparatus. The vibration propagates to an external apparatus through the piping and/or a portion of the solenoid valve contacting with the external apparatus. This phenomena is troublesome.
For eliminating this trouble, the solenoid valve in the prior art has a chamber in the middle of the piping. FIG. 7 shows a schematic diagram of an apparatus for suppressing the purge of the evaporated fuel gas in the prior art. The apparatus for suppressing the purge of the evaporated fuel gas comprises a canister 130. And a chamber 140 is disposed in the middle of the piping 150 connecting the solenoid valve 100 and the canister 130.
The function of the apparatus for suppressing the purge of the evaporated fuel gas in the prior art is explained below.
When the engine starts to rotate, a negative pressure appears in the intake manifold of the engine. Therefore, when the solenoid valve 100 is opened, evaporated gas from the canister 130 is supplied to the intake manifold, after passing through the chamber 140 and the solenoid valve 100.
If the supply amount of the purge gas is not appropriate, it causes bad influences to the function of the engine. Thus the solenoid valve 100 is controlled by a control signal from a controller (not shown) so as to be intermittently opened and closed, namely the duty ratio of the opening and closing of the solenoid valve is controlled. This intermittent opening and closing generates an operation sound and a flow sound. The sounds are damped by the chamber 140 for preventing the propagation to the canister 130, so that a generation of resonating sound in the canister 130 is eliminated. Simultaneously, the pulsation of flow in the piping is damped by the chamber 140, so that the vibration of the piping and the canister caused by the pulsation is eliminated.
FIG. 8 is a characteristic curve of sound emission versus the position of the chamber. FIG. (a) corresponds to the case that no frequency component in the propagating sound resonates in the piping, on the other hand, (b) corresponds to the case that a frequency component equal to the eigenfrequency of the canister resonates in the piping.
FIG. 9 shows a characteristic curve of resonating vibration of the canister versus the position of the chamber. FIG. (a) corresponds to the case that no frequency component in the propagating sound resonates in the piping, on the other hand, (b) corresponds to the case that a frequency component equal to the eigenfrequency of the canister resonates in the piping.
The canister used in the evaluation shown in FIGS. 8 and 9 had an eigenfrequency of 850 Hz, which corresponds to a wave length of 40 cm. FIGS. 8 and 9 show that a resonance appears when the piping length is an even number multiplied by a quarter of wave length (10 cm).
These figure show that a pulsation suppressing effect is small when the chamber 140 is arranged at an antinode of the vibration in the piping, and the effect appears when the chamber 140 is arranged at a node of the oscillation. Antinodes and nodes of the oscillation in the piping are schematically shown at the upper portion of the FIGS. 8(a), (b). It shall be noted that when both the ends of the piping, which is connected with the input port 103, are opened, both the ends are antinodes for all the frequency components, irrespective of the resonance.